The Digital Video Broadcasting-Terrestrial standard (DVB-T) utilises Orthogonal Frequency Division Multiplexing (OFDM) to communicate data representing video images and sound to receivers via a broadcast radio communications signal. There are known to be two modes for the DVB-T standard which are known as the 2 k and the 8 k mode. The 2 k mode provides 2048 sub-carriers whereas the 8 k mode provides 8192 sub-carriers. Similarly for the Digital Video Broadcasting-Handheld standard (DVB-H) a 4 k mode has been provided, in which the number of sub-carriers is 4096.
In order to improve the integrity of data communicated using DVB-T or DVB-H a symbol interleaver is provided in order to interleave input data symbols as these symbols are mapped onto the sub-carrier signals of an OFDM symbol. Such a symbol interleaver comprises an interleaver memory in combination with an address generator. The address generator generates an address for each of the input symbols, each address indicating one of the sub-carrier signals of the OFDM symbol onto which the data symbol is to be mapped. For the 2 k mode and the 8 k mode an arrangement has been disclosed in the DVB-T standard for generating the addresses for the mapping. Likewise for the 4 k mode of DVB-H standard, an arrangement for generating addresses for the mapping has been provided and an address generator for implementing this mapping is disclosed in European Patent application 04251667.4. The address generator comprises a linear feed back shift register which is operable to generate a pseudo random bit sequence and a permutation circuit. The permutation circuit permutes the order of the content of the linear feed back shift register in order to generate an address. The address provides an indication of a memory location of the interleaver memory for writing the input data symbol into or reading the input data symbol out from the interleaver memory for mapping onto one of the sub-carrier signal of the OFDM symbol. Similarly, an address generator in the receiver is arranged to generate addresses of the interleaver memory for writing the received data symbols into or reading the data symbols out from the interleaver memory to form an output data stream.
In accordance with a further development of the Digital Video Broadcasting-Terrestrial broadcasting standard, known as DVB-T2 there has been proposed that further modes for communicating data be provided.